The present invention relates to monitoring of the shaft doors of an elevator system.
Elevator systems of the conventional kind generally comprise shaft doors by which the elevator shaft can be separated from the adjoining areas in each floor. Many elevator systems additionally have car doors by which the elevator car is self-closing and which move together with the car from floor to floor. For reasons of safety all shaft doors must always be closed in operation with the exception of the shaft door of that floor in which the elevator car has just stopped. Equally, the car doors have to be closed when the elevator has not just stopped at a floor in order to allow loading or unloading or entering or leaving. For maintenance purposes the shaft and/or car doors can obviously also be opened when the elevator car is disposed elsewhere than in the above-described positions. The state, i.e. the setting of the shaft doors or the setting of locks by which the shaft door leaf or leaves is or are lockable in the closed setting thereof, is monitored with the help of monitoring systems. For this purpose sensor means, for example in the form of positively guided devices with safety contact positions, are provided. The safety contact positions are integrated in series connection in a safety circuit. The arrangement is realized in such a manner that the elevator car can be moved only when the safety circuit and thus also all safety contacts integrated therein are closed.
Monitoring systems with safety circuits of this kind are subject to numerous disadvantages which are briefly listed in the following:
Each safety circuit has inherent problems; belonging thereto are the length of the connections, the voltage drop in the safety circuit and the comparatively high assembly cost.
Individual safety contacts are relatively susceptible to fault; unnecessary emergency stops of the elevator system therefore frequently occur.
Notwithstanding a monitoring system with a safety circuit, unsafe and risky situations cannot be entirely avoided; on the one hand the safety contacts can individually or in common be bridged over relatively easily, which is virtually equivalent to placing the safety precautions out of action, and on the other hand an open shaft door does indeed prevent movement of the car, but if the car is not located at the shaft door just open the risk nevertheless exists of a fall through the open shaft door.
Intelligent or situationally appropriate reactions, for example in the case of interruption of the safety circuit, are not possible; in particular, it is not possible to avoid unintentional trapping of persons in the elevator car.
The monitoring system does not allow a specific diagnosis, i.e. if the safety circuit is opened it can only be established that at least one safety contact and thus at least one lock or at least one shaft door is open. However, it cannot be established which safety contact has opened. The monitoring system does not, before a fault in the safety circuit occurs, deliver any information allowing recognition of the state (wear, corrosion) of individual safety contacts or enable identification thereof. A state-dependent maintenance at an instant in time in which the elevator car can be shut down without problems is thus not assisted.
Serviceability of the elevator is limited, since an open safety contact always has the consequence of placing the elevator system out of operation even when another solution, for example blocking of the access region to a non-closable shaft door, would be possible.
A further disadvantage of known systems is that each shaft door leaf is provided with at least one electrical contact which has to be incorporated into the safety circuit. This approach is laborious and costly.
An improved system in which the state of the shaft doors is detected by way of a bus at the floor side and by way of a car bus is described in a European patent application with the title “Elevator system”. This application was filed on Sep. 18, 2001 and carries the application number 01810903.3. In the case of the monitoring system for an elevator described in this patent application the shaft doors and/or the car doors have sensor means by which the state thereof, i.e. the position of its door leaves, is detected. The monitoring system additionally comprises an evaluating system which is connected with the sensor means and which evaluates the signals delivered by the sensor means. This evaluation is carried out at short intervals in time and makes it possible to detect the state of the monitored shaft or car door leaf; equally, changes in the signal characteristic over time can be detected. According to this improved system, detection of the state of the shaft or car door leaf by the sensor means can be analyzed and is capable of diagnosis. Moreover, a gradual deterioration of individual subsystems is recognizable so that preventative maintenance can be initiated in good time.